In the United States alone, grain loss due to insect damage has been estimated to exceed about 1 billion dollars per year. The grain industry hopes to discover some means of detecting and accurately quantifying hidden insect or other infestation in grain.
For example, wheat stored in bulk is prone to develop a nearly invisible internal infestation by the wheat weevil, Sitophilus granarius, and closely related insects. The weevils tend to propagate in zones of wheat processing equipment that trap and hold grain long enough for these insects to thrive and spread. The solution to this infestation problem seems to be mainly a combination of the prevention and the early detection of infestation.
Because the life cycle of such insects may be as little as about one month, these grain weevils can multiply quickly enough to ruin large shipments of stored grain. Many methods have been proposed to detect this type of internal infestation. Detection of hidden infestation is quite important to the grain trading industry, but the various proposed and existing methods of detecting hidden wheat weevil infestation all have certain drawbacks.
Many methods of detecting hidden infestation have been proposed and used. These methods include the staining of material used to plug the egg holes, density separations, crushing kernels in ninhdrin impregnated paper, detection of carbon dioxide and uric acid, insect antibodies, x-rays, the audible detection of faint sounds emitted by internal larvae, NMR, insect antibody detection, etc. Most of these methods are quite complex or are tedious or lack necessary sensitivity. The antibody method, in particular, is quite sensitive but is too complex and takes too long to be widely used at the inspection site.
Grain industry brokers seek sensitive, accurate tests for hidden infestation of grain before purchase or transportation for later sale. Failure to detect infestation may lead to destruction of the entire lot of grain. Any inspection method that depends on visible assessment of damage will often miss internal insect infestation. Most of the commonly used methods, such as the insect-damaged kernal (IDK) test, are inaccurate and imprecise, often dependent on subjective judgments by human inspectors.
The US government promulgates standards based on visible inspection of the grain for insects and insect damage. For example, more than two live insects per kilogram of wheat or more than 32 infested grains in a more closely inspected 100 gram grain sample are the grading criteria in condemning wheat for human food use.
Each of the known methods of detecting wheat weevil infestations has certain drawbacks. Cracking and flotation is not very accurate, as indicated by the wide scatter in the data generated by different labs. Insect antibody detection is very sensitive and also accurate, but it is not easily adapted for rapid field use by unskilled workers. The same is the case with X-ray detection, which requires both expensive equipment and skilled operators. One proposed method uses passive near infrared spectra measurements; however, this method requires expensive equipment.
Almost all of the techniques currently employed for insect detection both fail to discriminate between live and dead insects and to detect internal insect infestation. It has been found that most of the commonly used methods of detecting infestation are inaccurate. (B. Brader, et al., A comparison of screening methods for insect contamination in wheat,J. Stored Products Res.: 38, pp. 75-86 (2002); G. E. Russell, Evaluation of four analytical methods to detect weevils in wheat; Granary weevil, Sitophilus granarius (L) in soft white wheat, J. Food. Protect.: 51, pp. 547-553 (1988).) In one study, while only 4% of wheat samples from 79 elevators were found to be infested by normal inspection, 16% of the samples were found to be infested after they were incubated from 4-6 weeks. (C. L. Storey, et al., Insect infestations in wheat and corn exported from the United States, J. Econ. Entomol.: 75, pp. 827-832 (1982).) Hidden infestation, then, is a common and important problem.